Having in mind that IR theories include FPA aspect, the main purpose of this paper is to examine the contribution of FPA in these theories. The necessity of this study become clearer when one acknowledges that FP makers should pay attention accurately to relationship between theory and practice in order to make successful rational decision in new complicated world. This enables them not only to have theoretical knowledge in FPA, but also extract some useful practical and policy – oriented prescriptions. In this article, through three sections, IR classic theories including Liberalism and Realism, micro, macro and middle – ground FP approaches and constructive IR theories are examined respectively. Finally the article concludes that IR theories are mutually constitutive and complementary, which means FP makers must avoid reductively relying on one of these theories.